Industrial gas turbines include a plurality of sensors that are used to monitor and control a gas turbine. Not all of the engine parameters can be measured or they can be measured only with reduced accuracy. Devised method outputs which estimate non-measured parameters such as efficiencies and flow capacities (so-called health parameters) for different engine components are typically used for health monitoring of gas turbine engines.
There exist many reasons for a variation of the health parameters. For example, the deviation of the health parameters is caused by manufacturing and assembly variation found in new built engines. On another hand, over the lifetime of operation, gas turbine components undergo some amount of degradation and this deterioration may be gradual or abrupt.
Some of the known deterioration mechanisms are seal and secondary flow leaks, clearance increases, erosion and fouling. While gas turbine health deterioration is a normal aging process that occurs in all engines as a result of usage, abrupt abnormal event such as foreign object damage are not predictable as they happen unexpectedly.
Various methods for monitoring the performance and the health of gas turbines have been devised in the past. Those methods are capable of providing diagnostic information such as the detection of engine fault or engine degradation and provide prognostic information such as the time the engine can be operated until maintenance procedures are required.
US 2007/214796 A discloses a method and system for monitoring a health of a combustion dynamics sensing system. Respective dynamic conditions of at least two combustor cans of a can annular combustor of a gas turbine engine are monitored with respective dynamic condition sensors associated with each of the cans. The method also includes establishing a baseline relationship between the respective dynamic conditions and then identifying a variance from the baseline relationship indicative of a degraded signal quality provided by a dynamic condition sensor associated with at least one of the cans.
U.S. Pat. No. 4,215,412 discloses a real-time gas turbine engine monitoring system is disclosed which includes a digital processor that utilizes a set of scalar coefficients and the current value of various engine operating parameters to predict the current value of a set of engine performance parameters. The actual values of these performance parameters are monitored and compared with the predicted values to supply deviation or error signals to monitor logic which provides an indication of faults within the digital processor, within the sensor units which provide the actual values of the monitored performance parameters and within the gas turbine engine. In addition, the deviation signals are utilized within the digital processor unit to determine a time dependent quadratic estimate of the temporal characteristics of each monitored engine parameter.
U.S. Pat. No. 6,466,858 discloses model-based trending process for a gas turbine engine that generates, in real-time, engine trend parameters from engine sensor data and ambient flight condition data to assess engine condition is described. The engine includes a plurality of sensors that are responsive to engine operations. The trending process is implemented using a commercially available processor coupled to the engine to monitor the engine operations, and having the desired processing speed and capacity. Engine health parameters are estimated and adjusted in a model for component diagnostics and fault detection and isolation.
U.S. Pat. No. 6,892,127 discloses a method and an apparatus for assessing damage to machine components is provided. The method includes calculating an expected parameter value based on a first parameter value indicator, calculating an estimate of an actual parameter value based on a second parameter value indicator, the second parameter value indicator being different than the first parameter value indicator, determining if the calculated expected parameter value is different than the calculated estimate of the actual parameter value by a predefined limit, and generating a damage flag based on a result of the comparison.
U.S. Pat. No. 8,050,843 discloses an estimation of a true health or independent parameter vector at time step uses the estimation of the true health or parameter vector at a previous time step as a starting value for the production of a predicted health parameter vector at time step. Based on the latter and a set of measured values of input variables of an extended model of the system, a prediction of output variables of the model is produced. This predicted model output is compared with measured values of the output variables to yield an error. From this error, a health parameter estimator in turn produces a health parameter estimate as a revision of the predicted health parameters.
DE 40 23 663 A1 discloses a diagnostic method. Vibration signals arising from the rotating parts of the machine are measured, prefiltered and digitized in a transient recorder. They are evaluated in a frequency range by frequency transformation. At least one characteristic value is obtained that represents the relation of the values of a harmonic frequency to a basic frequency over a predetermined period. A signal processor limits the frequency band and calculates the frequency function e.g. by a Fast-Fourier Transformation.